Rhenium

37.4 %

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62.6 %

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Powder

Risk

Powder

Rhenium is a chemical element with the chemical symbol Re and atomic number 75 in the periodic table of elements it is in the 7th group ( group 7) or manganese group. It is a very rare, silvery-white lustrous, heavy transition metal. Alloys with Rheniumanteilen are used in aircraft engines, in the manufacture of unleaded petrol and thermocouples.

Biological functions of rhenium are not known, it does not normally occur in the human organism. Similarly, no toxic effects of the metal are known, it is considered harmless as occupational hygiene.

• 9.1 oxides
• 9.2 halides
• 9.3 Other rhenium

History

The existence of the later rhenium was first predicted in 1871 by Dmitri Ivanovich Mendeleev as Dwi - Manganese. He graduated from the laws of the marketplace designed by him Periodic Table, below that of manganese two unknown elements that later technetium and rhenium are need.

Rhenium was discovered only in 1925 by Walter Noddack, Ida Tacke, and Otto Berg. They examined columbite to find the sought elements eka- manganese and Dwi. Since the desired elements were contained in the samples only to a very limited extent, they had to be enriched by separation of the other components. Finally, the subsequent rhenium could be detected by X-ray spectroscopy. Noddack and Tacke also claimed that very small amounts of the eka- manganese to have (later technetium ) found, but this could not be confirmed by representation of the item. They called the elements according to their home areas Rhenium (Latin Rhenus for Rhine ) and Masurium (of Masuria ). However, the latter set not by following the discovery of technetium 1937.

1928 could Noddack and Tacke first extract a gram of rhenium from 660 kg molybdenum ore. Because of the high cost of the production of significant amounts did not begin until 1950, when a greater need for newly developed tungsten -rhenium and molybdenum - rhenium alloys existed.

Occurrence

Rhenium is rarer than rhodium, ruthenium and iridium with a share of only 0.7 ppb in the Earth's continental crust. It's not dignified, but only bound in some ores. Since rhenium has similar properties as molybdenum, it is mainly found in molybdenum ores such as molybdenite MoS2. These may contain up to 0.2% rhenium. More rhenium-containing minerals are columbite (Fe, Mn) [ NbO3 ], Gadolinit Y2 Fe loading [O | SiO 4 ] 2 and Alvit ZrSiO4. Also in the Mansfeld Kupferschiefer rhenium is present in small amounts. The largest deposits of rhenium-containing ores are located in the United States, Canada and Chile.

To date, only a Rheniummineral, the Rheniit ( rhenium (IV ) sulphide, ReS2 ) was discovered. The site lay in a fumarole at the summit crater of the volcano Kudrjawyj (Russian: Кудрявый ) on the island Iturup, which belongs to the Kuril Islands (Russia).

Production and representation

The raw material for the extraction of rhenium molybdenum ores, especially molybdenite. If these are roasted in the course of refining molybdenum, rhenium accumulates as a volatile rhenium (VII ) oxide in the fly ash. This can with water containing ammonia to ammonium perrhenate ( NH4ReO4 ) are implemented.

The ammonium perrhenate is then reduced with hydrogen at high temperatures to elemental rhenium.

The main producers in 2006 were Chile, Kazakhstan and the United States, the total amount of produced rhenium amounted to about 45 tons.

Properties

Physical Properties

Rhenium is a white shiny hard heavy metal which is similar to the outside of palladium and platinum. It crystallizes in a hexagonal closest packing of spheres in space group 6/mmm with the lattice parameters a = 276.1 pm and c = 445.8 pm and two formula units per unit cell. The density of rhenium 21.03 g/cm3 is only surpassed by the three platinum metals osmium, iridium and platinum.

Rhenium has with 3186 ° C one of the highest melting points of all elements. It is only by the refractory metal tungsten ( 3422 ° C ) and carbon exceeded. However, the boiling point is the highest of all metals 5596 ° C and exceeds tungsten ( boiling point 5555 ° C) at 41 K.

Below 1.7 K rhenium is the superconductor.

Rhenium can be good by forging and welding process because it is ductile and in contrast to tungsten or molybdenum is retained even after recrystallization. When welding rhenium is no embrittlement, which would lead to a higher brittleness and thus poorer material properties.

The activity of the rhenium is 1.0 MBq / kg.

Chemical Properties

Although rhenium is not one having a negative standard potential to the noble metals, it is stable at room temperature and non-reactive to air. Only when heated it reacts with oxygen from 400 ° C to rhenium (VII ) oxide. Even with the non-metals, fluorine, chlorine, and sulfur reacts when heated.

In non-oxidizing acids such as hydrochloric acid or hydrofluoric acid, rhenium is not soluble. In contrast, the oxidizing sulfuric and nitric acid rhenium solve easily. With oxidation melts easily form colorless perrhenate (VII ) of the form ReO4 or green rhenates (VI ) of the type - ReO42.

Isotopes

There are a total of 34 known isotopes and further 20 Kernisomere of rhenium. Of these two come the isotopes 185Re and 187Re, naturally. 185Re, which is present in a proportion of 37.40 % to the natural isotope distribution, is the only stable isotope. The more frequent with a share 62.60 % 187Re is weakly radioactive. It decays by beta decay with a half-life of 4.12 · 1010 years to 187Os, which leads to a specific activity of 1020 becquerels / gram. Rhenium is so beside indium one of the few elements which, while having a stable isotope, but most commonly found in nature in its radioactive form. Both isotopes are detectable with the aid of nuclear magnetic resonance spectroscopy. Of the artificial isotopes 186Re and 188Re are used as tracers. As a principal beta emitters 186Re is used in nuclear medicine for therapy in radiation synovectomy. 188Re serves as a radiopharmaceutical for tumor therapy.

The decay of 187Re to 187Os is used as rhenium - osmium method in geology for isotopic age determination of rocks or minerals. The Isochronenmethode is used for correction of the pre-existing osmium.

→ List of rhenium isotopes

Use

Rhenium is usually not used elementary, but used as an additive in a variety of alloys. About 70 % of the rhenium is used as an additive in nickel superalloys. An addition of 4 to 6% rhenium is effective for improving the creep resistance and fatigue properties at high temperatures. These alloys are used as turbine blades for aircraft engines.

A further 20 % of the rhenium produced is used for platinum- rhenium catalysts. These play a major role in increasing the octane number of unleaded gasoline by reforming ( " Rheniforming "). The advantage of the rhenium is that it compared with pure platinum not quickly by carbon deposits on the surface of the catalyst ( " coking "), is deactivated. This makes it possible to carry out production at lower temperatures and pressures and to produce as efficient. Other hydrocarbons, such as benzene, toluene and xylene can be produced with platinum -rhenium catalysts ..

Thermocouples for temperature measurement at high temperatures ( up to 2200 ° C) are made of platinum -rhenium alloys. And as an alloy with other metals, such as iron, cobalt, tungsten, molybdenum, rhenium or precious metals improves the resistance to heat and chemical attack. The application is limited by the rarity and the high price of rhenium.

In some special applications Rhenium is also used, for example for thermionic cathodes in mass spectrometers or contacts in electrical switches.

Proof

There are several ways to detect rhenium. One possibility spectroscopic methods. Rhenium has a pale green flame color with characteristic spectral lines at 346 and 488.9 nm Gravimetric rhenium is about the characteristic crystallizing perrhenic or different perrhenate salts, such tetraphenylarsonium perrhenate, detectable. Also modern analytical methods such as mass spectrometry or nuclear magnetic resonance spectroscopy are suitable for the detection of the member.

Safety

How many metals rhenium is in powder form and highly inflammable. To clear water must not be used because of the resulting hydrogen. Instead, to be used as extinguishing agents Extinguishing powder or metal fire extinguisher. Compact rhenium, however, is non-flammable and dangerous. Rhenium has no known biological role for the human organism. Although on the toxicity of rhenium nothing accurate is known and no toxicity values ​​exist, rhenium occupational hygiene is considered safe.

Compounds

Rhenium is a large number of connections; as manganese, technetium and compounds in the oxidation states III to VII are known. In contrast to manganese compounds, however, are more stable than in the lower in the high oxidation states.

Oxides

There are a total of five oxides of rhenium known, the yellow Re.sub.2O.sub.7, red ReO3, Re2O5, brown black ReO2 and Re2O3. Rhenium (VII ) oxide, rhenium oxide Re2O7 is the most stable. It is an intermediate in the Rheniumgewinnung and can be used as starting compound for the synthesis of other rhenium compounds, such as methyltrioxorhenium. In water it dissolves to form the stable perrhenic HReO4. Rhenium ( VI) oxide ReO3 has a characteristic crystal structure, the crystal structure is used as type ( rhenium trioxide type).

Halides

A total of 13 compounds of the rhenium to the halogens fluorine, chlorine, bromine and iodine is known. Here rhenium reacts preferentially to Hexahalogeniden type ReX6. The result is a pale yellow rhenium (VI ) fluoride ReF6 and green rhenium (VI ) chloride ReCl6 directly from the elements at 125 ° C and 600 ° C. Reaction of rhenium with fluorine under light pressure at 400 ° C leads to a light yellow rhenium (VII ) fluoride, in addition to osmium ( VII), and iodine fluoride (VII ) fluoride, the only known halide in the oxidation state VII Reddish brown rhenium (V ) chloride ( ReCl5 ) 2 has a dimeric, octahedral structure. ReO2 chlorinating with thionyl chloride yields a black polymeric Re2Cl9 chloride, which consists of chains of dimer re- Cl - clusters which are bridged by chlorine atoms. If higher Rheniumchloride thermally decomposed at about 550 ° C, dark red, trimeric rhenium (III ) chloride Re3Cl9 forms. Structurally, the molecules of triangular metal clusters, where the Re-Re distances of 248 pm double-bond character of the metal -metal bonds prove. The halides are sensitive to water and react with water to halogen oxides or oxides.

More rhenium

The black rhenium (VII ) sulfide Re2S7 arises from Perrhenatlösungen by introducing hydrogen sulfide. Thermal decomposition also results in black rhenium (IV ) sulphide ReS2, which is also accessible directly from the elements.

Forming a plurality of rhenium complexes. There are known both classical complexes with different metal centers, as well as metal clusters. In these rhenium -rhenium multiple bonds are partly present in the form of triple or quadruple bonds. A four -bond exists as the Re2X82 - complex ion (X is a halogen atom or a methyl group).

Organometallic compounds of rhenium are known. An important organic rhenium is methylrhenium trioxide (MTO ) can also be used as a catalyst for metathesis reactions for epoxidation of olefins and for the olefination of aldehydes. MTO and other rhenium catalysts for metathesis are highly resistant to catalyst poisons.

→ Category: rhenium